DE102019104556A1 - Method and device for determining optical properties of a sample material - Google Patents

Abstract

The invention relates to a method (100), preferably a spectroscopy method, more preferably an ATR infrared spectroscopy method, for determining optical properties of a sample material (5), the method (100) comprising the following steps: determining (101) a first intensity of the Sample material (5) reflected light (3r) of a first polarization state; Determining (102) a second intensity of the light (3r) reflected by the sample material (5) in a second polarization state (102); Ratio formation (103) of the first intensity and the second intensity or vice versa. The invention also relates to a device (1), preferably a spectrometer, more preferably an ATR infrared spectrometer, for determining optical properties of a sample material (5) comprising at least one detector device (8, 8a, 8b) for determining a first intensity of the sample material (5) reflected light (3r) of a first polarization state and for determining a second intensity of the light (3r) reflected from the sample material (5) of a second polarization state and at least one arithmetic unit (11) for forming the ratio of the first intensity and the second intensity or vice versa .

Description

The invention relates to a method and a device for determining optical properties of a sample material.

Optical properties of a sample material are often determined by means of spectroscopic measuring methods such as spectroscopy on the basis of attenuated total reflection (ATR or frustrated total internal reflection, FTIR) on the basis of attenuated and / or frustrated or prevented total reflection. The advantage of such spectroscopic methods is in particular that an absorption spectrum can be recorded despite a strong basic absorption of the sample material. It is known that the attenuation of the light wave on the surface between an ATR element and the sample material is different for different polarizations of the incident light wave and that the different polarizations also have a different phase offset.

For example, from the US 7,920,264 B1 a HATR method (horizontal attenuated total reflection, HATR) is known, which uses the phase offset for two different polarization directions to measure the rotation of the polarization plane through the sample material, i.e. for polarimetry.

Thermal emitters, which are filtered with a monochromator for wavelength selection, are often used as light sources for such spectroscopic methods. However, thermal radiators have the disadvantage that they have a low spectral power density and therefore a low intensity with narrow-band filtering. Alternatively, laser sources such as quantum cascade lasers are also used in the above-mentioned spectroscopic methods. Although these represent very powerful light sources, especially in the middle and far infrared wavelength range, they have a high intensity noise compared to thermal radiators, so that the sensitivity is reduced, especially in the case of sample material with low concentrations of the substance to be examined, and these are therefore no longer measured can. The power density of these light sources is also not constant over the wavelength, so that the measured spectrum has to be compared with a reference measurement, in particular without or with known sample material. Here it is possible to record the reference measurement simultaneously directly through an additional optical path and to subtract it from the measurement signal (balanced detection). The disadvantage of such an additional reference path is that it could also have a wave-dependent transmission and is also subject to fluctuations other than the measurement path. The reference path should also preferably have attenuation similar to that of the measurement path.

The invention is based on the object of providing a method and a device for determining optical properties of a sample material which avoid the disadvantages of the prior art. In particular, the invention is also based on the object of providing an improved method and an improved device for determining optical properties of a sample material, which advantageously reduces or suppresses and / or eliminates the effects of the intensity noise of light sources.

This object is achieved by a method, preferably a spectroscopy method, more preferably an ATR infrared spectroscopy method, for determining optical properties of a sample material, which comprises the following steps: a) determining a first intensity of light of a first polarization state reflected from the sample material; b) determining a second intensity of the light of a second polarization state reflected by the sample material; c) Formation of the ratio of the first intensity and the second intensity or vice versa. This object is further achieved by a device, preferably a spectrometer, more preferably an ATR infrared spectrometer, for determining optical properties of a sample material, comprising: at least one detector device for determining a first intensity of light of a first polarization state reflected by the sample material and for determining a second intensity of the light of a second polarization state reflected from the sample material; - At least one arithmetic unit for forming the ratio of the first intensity and the second intensity or vice versa.

In particular, the method according to the invention, preferably according to one of claims 1 to 12, is carried out by means of the device. It is thus possible if the device is used to carry out a method according to one of Claims 1 to 12. It is also advantageous if step c) is carried out after steps a) and b).

The invention is based on the knowledge that by determining a first intensity of the light reflected by the sample material of a first polarization state, by determining a second intensity of the light reflected by the sample material of a second polarization state and by subsequently forming the ratio of the first intensity and the second intensity or vice versa the effects of the Intensity noise from light sources on the measurement result can be reduced or suppressed and / or eliminated. The invention uses the polarization dependency of the light reflected from the sample material, in particular that formed at the interface from the sample material and a reflection element, with in particular the different polarizations of the reflected light having relative changes in the reflection of different degrees. It has surprisingly been found here that, despite the formation of the ratio of the intensities of the reflected light of the two polarization states, a signal remains, with the intensity noise of the light source used not being included in the final signal. This eliminates the need for a reference path. Fluctuations, which are caused by the measurement setup itself, are also not included in the signal, in particular as long as they affect both polarization states in the same way.

“State of polarization”, “type of polarization”, “direction of polarization”, “degree of polarization” and / or “polarization” are preferably understood to mean the direction of oscillation of light. In particular in the wave model, light is preferably a wave oscillating perpendicular to its direction of propagation, in particular a transverse wave, so that these terms are preferably understood here to mean the direction of oscillation of a transverse wave. The direction of oscillation preferably relates to the field vector of the electric field, in particular the field vector of the magnetic field oscillating perpendicular thereto. In particular, if the direction of oscillation changes quickly and in a disorderly manner, it is preferably unpolarized light. The terms “state of polarization”, “type of polarization”, “direction of polarization”, “degree of polarization” and / or “polarization” therefore particularly indicate the ordered proportion.

It is also possible that the method, preferably a spectroscopy method, more preferably an ATR infrared spectroscopy method, a HATR infrared spectroscopy method, a FEWS infrared spectroscopy method (English fiber evanescent wave spectroscopy, FEWS) and / or an FTIR infrared spectroscopy method. It is also possible that the device is preferably a spectrometer, more preferably an ATR infrared spectrometer, a HATR infrared spectrometer, a FEWS infrared spectrometer and / or an FTIR infrared spectrometer.

It is possible that the sample material is liquid and / or solid. It is thus possible for the sample material to include, for example, water, bacteria and / or solids. Furthermore, it is conceivable that the sample material contains one or more substances selected from the group: water, bacteria, viruses, solids, solvents, solvent mixtures, lacquer layers, polymer films, thermosetting plastics, body fluids, in particular blood, mono- or multicellular organisms, fungi, plants, in particular algae.

Further advantageous embodiments of the invention are specified in the subclaims.

The method preferably further comprises the following step, in particular which is carried out before steps a) and b): splitting the light reflected from the sample material into the first polarization state and the second polarization state, preferably by means of at least one polarizer, more preferably by means of a first polarizer and a second polarizer.

It is also advantageous if the device further has at least one polarizer, in particular for dividing the light reflected from the sample material into the first polarization state and the second polarization state, in particular that the device has a first polarizer for dividing the light reflected from the sample material into the first polarization state and a second polarizer for splitting the light reflected from the sample material into the second polarization state.

“Polarizer (s)” are preferably understood to mean components which filter out electromagnetic waves, in particular light such as light from the infrared wavelength range, of a certain polarization from non-polarized, partially or differently polarized electromagnetic waves. It is possible here for polarizers to use mechanisms selected from the group: dichroism, reflection, birefringence, scattering and / or diffraction in order to separate the different polarizations of the incident waves. For example, polarizers that separate a linearly polarized electromagnetic wave, linear polarizers, or also linear polarizers, are mentioned in particular. Furthermore, for example, polarizers that separate circularly polarized light are referred to as circular polarizers.

The at least one polarizer, in particular the first polarizer and the second polarizer, is advantageously selected from the group: polarizer based on birefringence, preferably polarizing prism, more preferably Nicol's prism, Rochon prism, Glan-Thomson prism, polarizer based on dichroism, preferred J-foil and / or H-foil, and / or polarizer based on reflection, preferably Brewster window.

The at least one polarizer, in particular the first polarizer and the second polarizer, is preferably a Brewster window. This makes it possible to separate the first and the second polarization state of the light reflected from the sample material, in particular it is ensured that further polarization states do not interfere with the measurement result.

It is also advantageous if the first and second polarization states differ, in particular if the first and second polarization states are linearly polarized states with mutually perpendicular oscillation planes, the first polarization state preferably being parallel polarized light and the second polarization state being perpendicularly polarized light or vice versa . This makes it possible to obtain a maximum possible signal, preferably for the ratio of the first intensity and the second intensity, in particular wherein these polarization states can also be separated well by means of the polarizers mentioned above.

It is also possible that in steps a) and / or b) the intensity of the light of the first and / or second polarization state reflected by the sample material is determined by means of at least one detector device, in particular that in steps a) and / or b ) the intensity of the light of the first polarization state reflected by the sample material is determined by means of a first detector device and the intensity of the light of the second polarization state reflected by the sample material is determined by means of a second detector device.

It is also possible for the device to have a first detector device for determining the first intensity of the light of the first polarization state reflected from the sample material and a second detector device for determining the second intensity of the light of the second polarization state reflected from the sample material.

The at least one detector device, in particular the first and / or the second detector device, is preferably a photodetector selected from the group: photocell, photomultiplier, microchannel plate photomultiplier, CMOS sensor, CCD sensor, photodiode, phototransistor, photoresistor, and / or thermal radiation meter, in particular bolometer, pyroelectric sensor, pyrometer, thermocouple and / or Golay cell.

Photomultipliers or photodiodes, such as an HgCdTe photodiode, are preferably used, particularly when there is little light to be detected and high temporal resolutions.

Furthermore, it is possible for the at least one detector device, in particular the first and / or the second detector device, to be a synchronous detector (lock-in). This makes it possible to further improve the noise suppression or to filter the noise further.

It is useful if the method further has the following step, in particular which is carried out before steps a) and b): Radiation of light onto the sample material through a reflection element in such a way that the light is formed at the interface from the sample material and the reflection element is reflected, in particular is totally reflected.

The light reflected by the sample material, in particular of the first and / or the second polarization state, is preferably the light that is reflected, in particular totally reflected, at the interface formed by the sample material and the reflection element. It is therefore advantageous if the light reflected from the sample material and the reflection element at the interface is the light reflected from the sample material, in particular the first and / or the second polarization state. It is advantageous if the light reflected from the sample material corresponds to the light reflected at the interface from the sample material and the reflection element or is identical to it.

In this case, the light is preferably radiated onto the sample material through the reflection element in such a way that an electromagnetic wave is formed on the surface of the reflection element and penetrates the sample material, in particular with the field strength of the electromagnetic wave decreasing exponentially. The electromagnetic wave on the surface of the reflection element, in particular the field strength of which decreases exponentially, is a so-called evanescent wave, which is preferably formed from the sample material and the reflection element during total reflection at the interface.

It is thus possible that, in particular within the reflection element, the angle (α) at which the light is irradiated onto the sample material is equal to the angle (β) at which the light is reflected from the sample material.

Here it is possible that, in particular within the reflection element, the angle (α) at which the light is irradiated onto the sample material and the angle (β) at which the light is reflected from the sample material, between 0 ° and 90 °, preferably between 10 ° and 85 °.

It is also advantageous if the refractive index of the reflective element (n ₁ ) is greater than the refractive index of the sample material (n ₂ ).

It is thus possible that the refractive index of the reflection element (n ₁ ) is between 2.0 and 4.0, preferably between 2.4 and 2.6, and / or that the refractive index of the sample material (n ₂ ) is between 1.05 and 1.95, preferably between 1.25 and 1.75.

Furthermore, it is useful if the angle (α) is greater than or equal to the angle for which total reflection occurs at the interface formed from the sample material and the reflection element, in particular for the light irradiated on the sample material.

In particular, the critical angle (Θ _c ) from which total reflection occurs is calculated as follows: $${\mathrm{\Theta }}_{\text{c}}=\text{arcsin}\left({\text{<figure-callout id="2" label="n" filenames="DE102019104556A1\_0006.png,DE102019104556A1\_0008.png" state="{{state}}">n</figure-callout>}}_2/{\text{n}}_1\right).$$

The critical angle (Θ _c ) is also referred to here in particular as the critical angle. From the critical angle (Θ _c ), the electromagnetic wave, in particular the irradiated light, can preferably no longer penetrate the optically thinner medium, in particular the sample material, and is instead at the interface between the optically denser and the optically thinner medium, in particular on the interface formed from the sample material and the reflection element, reflected, in particular totally reflected. In particular, the angle of reflection is the same as the angle of incidence.

It is thus possible that the light irradiated onto the sample material, in particular due to the angle (α) at which the light is irradiated onto the sample material, is unable to propagate in the sample material.

The reflection element is advantageously an optical waveguide, in particular an optical waveguide, in which light is guided due to total reflection. For example, such an optical waveguide is a prism or a fiber, in particular without a jacket.

The reflection element is preferably an ATR element, in particular an ATR crystal.

So it is possible that the reflection element, preferably the ATR element, more preferably the ATR crystal, zinc selenide (ZnSe), germanium (Ge), thallium bromide iodide (KRS-5), silicon (Si), AMTIR (amorphous material transmitting infrared radiation), in particular AMTIR-1 (GeAsSe), and / or diamond. Such materials are preferably suitable for light from the infrared wavelength range.

Furthermore, it is also conceivable that, in particular in the case of FEWS infrared spectroscopy methods and / or in a FEWS infrared spectrometer, the ATR element comprises chalcogenide glass fibers.

It is also useful if the light irradiated onto the sample material is unpolarized light, preferably when the light irradiated onto the sample material has a polarization of less than 45 ° to the plane of incidence. In this way, in particular, uniform excitation in perpendicular and parallel polarization is achieved.

The light irradiated onto the sample material is advantageously light from the infrared wavelength range, preferably from the near and / or the middle and / or the far infrared range, more preferably light from the wavelength range between 0.8 μm and 1000 μm, even more preferably light from the wavelength range between 2.5 µm and 25 µm, furthermore preferably light from the wavelength range between 8 µm and 12 µm.

The light radiated onto the sample material is expediently emitted by a light source, in particular where the light source is selected from the group: lasers, preferably semiconductor lasers, more preferably quantum cascade lasers (QCL), and / or thermal emitters, preferably incandescent lamps, Nernst lamps, resistance heating elements Silicon carbide or carbon arc lamp. It is also possible to use other light sources. In particular, the method and / or the device for determining optical properties of a sample material is not subject to any restriction with regard to the light sources used.

It is also expedient if the device further comprises one of the following units: a light source, in particular for irradiating light onto the sample material through a reflection element in such a way that the light is reflected at an interface formed from the sample material and the reflection element, in particular is totally reflected; a reflection element, preferably an ATR element, more preferably an ATR crystal, in particular wherein the sample material forms an interface with the reflection element; a fixing unit for fixing the sample material on the reflective element; - one or more optical waveguides, preferably one or more fibers, more preferably one or more glass fibers, in particular for guiding the light irradiated onto the sample material and / or the light reflected from the sample material; - One or more mirrors, in particular for deflecting the light; - at least one optical sump; one or more wavelength selectors, preferably one or more monochromators, in particular for the spectral isolation of a predetermined wavelength, preferably the light irradiated onto the sample material.

It is also possible if the light irradiated onto the sample material and / or the light reflected from the sample material, in particular the first and / or the second polarization state, is a light beam, preferably the light beam having a beam diameter between 10 μm and 10,000 μm at least in some areas having.

Furthermore, it is also possible that the light irradiated onto the sample material and / or the light reflected from the sample material, in particular of the first and / or the second polarization state, at least regionally in an optical waveguide, preferably in a fiber, even more preferably in a glass fiber , to be led.

It is advantageous if in step c) the effects of the intensity noise of the light source, in particular on the measurement result, are reduced, preferably eliminated, due to the formation of the ratio of the first intensity and the second intensity or vice versa.

It is thus possible that the effects of the intensity noise of the light source, in particular on the measurement result, by at least a factor of 2.5, preferably by a factor of 5 , more preferably by the factor 10 , even more preferably by the factor 50 , furthermore preferably by the factor 100 , be reduced.

It is also useful if at least steps a) to c) for light from the infrared wavelength range, preferably from the near and / or the middle and / or the far infrared range, more preferably for light from the wavelength range between 0.8 μm and 1000 µm, even more preferably for light from the wavelength range between 2.5 µm and 25 µm, and even more preferably for light from the wavelength range between 8 µm and 12 µm.

Furthermore, it is preferred that the light paths in step a) and b), in particular for the light of the first and second polarization states reflected by the sample material, are essentially identical. It is thus also possible for the light paths in step a) and b) to be identical, in particular for the light of the first and second polarization states reflected from the sample material. In particular, this ensures that fluctuations have the same effect on both measurement paths.

It is also possible for the light paths in step a) and b) to differ by less than 10 mm, preferably by less than 1 mm. In particular, such small differences arise in the light paths due to the measurement setup with a first and a second detector device, so that small differences can arise in the light paths particularly at the end of the measurement section.

Steps a) and b) preferably take place simultaneously, in particular the intensity of the light of the first and second polarization states reflected by the sample material is determined simultaneously. This makes it possible in particular that there is no need for an additional reference measurement. Furthermore, an exact measurement result is achieved in this way, since possible differences between the signals, which can arise due to measurements that are offset in time, are eliminated.

It is also possible to use the method described above, in particular according to one of Claims 1 to 12, and / or the device described above, in particular according to one of Claims 13 to 15, for the spectral analysis, in particular of the sample material. The spectral analysis, in particular of the sample material, is preferably based on total reflection, preferably frustrated total reflection.

So it is also possible that the method described above, in particular according to one of claims 1 to 12, and / or the device described above, in particular according to one of claims 13 to 15, for or for the suppression of the intensity noise of light sources, in particular in spectral analysis.

• 1 zeigt schematisch einen bekannten Messaufbau in Draufsicht
• 2a und 2b zeigen schematisch eine Vorrichtung in Seitenansicht und in Draufsicht
• 3a zeigt schematisch einen vergrößerten Ausschnitt der 2a
• 3b zeigt schematisch einen vergrößerten Ausschnitt der 3a
• 4a bis 4c zeigen Diagramme
• 5a bis 5c zeigen schematisch Vorrichtungen in Seitenansicht und in Draufsicht
• 6 und 7 zeigen schematisch Verfahrensschritte zur Bestimmung optischer Eigenschaften eines Probenmaterials

In the following, exemplary embodiments of the invention are exemplified with the aid of the enclosed, not to scale 2 to 7th explained.

• 1 shows schematically a known measurement setup in plan view
• 2a and 2 B show schematically a device in side view and in plan view
• 3a shows schematically an enlarged section of FIG 2a
• 3b shows schematically an enlarged section of FIG 3a
• 4a to 4c show diagrams
• 5a to 5c show schematically devices in side view and in plan view
• 6th and 7th schematically show method steps for determining optical properties of a sample material

1 shows schematically a measurement setup known from the prior art 1000 in plan view. Preference is given by means of the measurement setup 1000 the optical properties of a sample material 5 certainly.

As in 1 shown includes the measurement setup 1000 a light source 2 , a beam splitter 4th , the sample material 5 , a mirror 6th , a variable attenuator 7th and two detectors 8a and 8b .

As a light source 2 In particular, thermal emitters that are filtered with a monochromator for wavelength selection are used. However, thermal emitters have the particular disadvantage that they have a low spectral power density and therefore a low intensity with narrow-band filtering. Alternatively used as a light source 2 laser sources such as quantum cascade lasers are also used. Although these represent, in particular, very powerful light sources in the middle and far infrared wavelength range, they have a high intensity noise compared to thermal radiators, so that particularly with sample material 5 with low concentrations of the substance to be examined, the sensitivity is reduced and this can therefore no longer be measured. The power density of such light sources is also 2 Not constant over the wavelength, so that the measured spectrum is advantageously carried out with a reference measurement, in particular without or with known sample material 5 to be compared.

For this purpose, it is preferred, as in 1 shown, according to the state of the art, an additional optical path is integrated into the measurement setup, so that the reference measurement can be recorded simultaneously directly through the additional optical path and can be subtracted from the measurement signal (balanced detection). As in 1 shown, especially the light 3 with the help of the beam splitter 4th split and passed into the reference path and the measurement path. In order to obtain an attenuation that is as identical as possible in the measurement path and in the reference path, the reference path in the prior art preferably comprises a variable attenuator 7th . The measurement signal and the reference signal are then advantageously in the detectors 8a and 8b , which are, for example, photomultipliers, are detected and subtracted from one another. A disadvantage of such an additional reference path, however, is that it could also have a wave-dependent transmission and is also subject to other fluctuations such as the measurement path. The reference path should also preferably have attenuation similar to that of the measurement path, which, however, is mostly only roughly by means of the variable attenuator 7th can be achieved as the sample material 5 is unknown.

In the following, preferred exemplary embodiments of the invention are exemplified with the aid of the enclosed, not to scale 2 to 7th explains in particular which avoid the disadvantages of the prior art and which advantageously reduce or suppress and / or eliminate the effects of the intensity noise of light sources.

2a and 2 B show schematically a device 1 in side view and top view.

As in 2a and in 2 B shown comprises the device 1 a light source 2 , Mirror 6th , a reflective element 9 , at least one polarizer 10 and at least one detector device 8th as well as a computing unit 11 .

The ones in the 2a and 2 B shown device 1 , preferably a spectrometer, more preferably an ATR infrared spectrometer, for determining optical properties of the sample material 5 comprises here: at least one detector device 8th for determining a first intensity of the sample material 5 reflected light 3r a first polarization state and for determining a second intensity of the sample material 5 reflected light 3r a second polarization state; - at least one computing unit 11 to form the ratio of the first intensity and the second intensity or vice versa.

The light source is preferred 2 selected from the group: lasers, preferably semiconductor lasers, more preferably quantum cascade lasers (QCL), and / or thermal emitters, preferably incandescent lamp, Nernst lamp, heating element made of silicon carbide or carbon arc lamp. The light source preferably emits light from the infrared wavelength range, preferably from the near and / or the middle and / or the far infrared range, more preferably light from the wavelength range between 0.8 µm and 1000 µm, even more preferably light from the wavelength range between 2 , 5 µm and 25 µm, furthermore preferably light from the wavelength range between 8 µm and 12 µm.

In the 2a and 2 B shown light source 2 it is, for example, a quantum cascade laser that emits light from the wavelength range between 8 µm and 12 µm.

As in the 2a and 2 B is shown, in particular, that of the light source 2 emitted light on a sample material, which is on the reflective element 9 is arranged, irradiated. For the sake of clarity, the sample material is not shown here. The light source is used to irradiate the sample material 2 emitted light especially with the help of the mirror 6th diverted. The reflection element also affects the sample material 9 irradiated light 3e preferably irradiated in such a way that the light is formed at the interface from the sample material and the reflection element 9 is reflected, in particular is totally reflected. It is preferably the one formed at the interface from the sample material 5 and the reflective element 9 reflected, in particular totally reflected, light around that of the sample material 5 reflected light 3r . With regard to the reflection at the interface, formed from the sample material and the reflection element 9 is here on the statements below in the context of 3a and the 3b referenced.

The light reflected from the sample material 3r is then, as also in 2a and 2 B shown by means of another mirror 6th to at least one polarizer 10 steered.

Using the polarizer 10 is preferably the light reflected from the sample material 3r divided into the first polarization state and the second polarization state.

The polarizer is advantageous 10 selected from the group: polarizer based on birefringence, preferably polarizing prism, more preferably Nicol's prism, Rochon prism, Glan-Thomson prism, polarizer based on dichroism, preferably J-foil and / or H-foil, and / or polarizer based on Reflection, preferably Brewster window.

It is advantageous here if the first and second polarization states differ, in particular if the first and second polarization states are linearly polarized states with mutually perpendicular oscillation planes, the first polarization state preferably being parallel polarized light and the second polarization state being perpendicularly polarized light.

The in 2a and 2 B shown polarizer 10 it is, for example, a linear polarizer, in particular which can sequentially filter out light in two linearly polarized states with mutually perpendicular oscillation planes as a function of a controllable state.

Then, in particular, the intensity of the light reflected from the sample material is determined 3r the first polarization state and the intensity of the light reflected from the sample material 3r of the second polarization state, as in 2a and in 2 B shown by means of the detector device 8th certainly.

The detector device is preferred here 8th a photodetector selected from the group: photocell, photomultiplier, microchannel plate photomultiplier, CMOS sensor, CCD sensor, photodiode, phototransistor, photoresistor, bolometer, pyroelectric sensor, pyrometer, thermocouple and / or Golay cell. At the in 2a and 2 B detector device shown 8th it is, for example, a photomultiplier.

In the in 2a and 2 B computing unit shown 11 then becomes the ratio of the intensity of the light reflected from the sample material 3r the first polarization state and the intensity of the light reflected from the sample material 3r of the second polarization state is formed.

This is preferred for a large number of wavelengths, in particular for light from the infrared wavelength range, preferably from the near and / or the middle and / or the far infrared range, more preferably for light from the wavelength range between 0.8 µm and 1000 µm, even more preferably for light from the wavelength range between 2.5 μm and 25 μm, and even more preferably for light from the wavelength range between 8 μm and 12 μm.

In the 2a and 2 B shown device 1 determined in particular as a function of the controllable state of the polarizer 10 for example, first the intensity of the light reflected from the sample material 3r the first polarization state and then the intensity of the light reflected from the sample material 3r of the second polarization state. In particular as soon as the intensities of the light reflected from the sample material 3r are determined for both polarization states, the ratio of these intensities is determined by means of the computing unit 11 educated. To this end, the computing unit 11 preferably a (working) memory and / or a microprocessor. In other words, the in 2a and 2 B shown device 1 preferably sequentially, in particular as a function of the controllable state of the polarizer 10 which, for example, filters out or allows parallel polarized light to pass through in a first controllable state and filters out or allows perpendicularly polarized light to pass in a second controllable state.

As in 2a and 2 B can be seen, in particular, are the light paths for determining the intensities for the sample material reflected light of the first and second polarization states identical.

In particular due to the formation of the ratio of the intensities of the light reflected from the sample material 3r for both polarization states the effects of the intensity noise of the light source 2 reduced, preferably eliminated.

For example, it is possible that the effects of the intensity noise of the light source 2 at least by a factor of 2.5, preferably by a factor 5 , more preferably by the factor 10 , even more preferably by the factor 50 , furthermore preferably by the factor 100 , be reduced.

It is also possible that the light irradiated onto the sample material 3e and / or the light reflected from the sample material 3r , in particular the first and / or the second polarization state, at least in some areas in an optical waveguide, preferably in a fiber, even more preferably in a glass fiber.

It is also possible that the light irradiated onto the sample material 3e and / or the light reflected from the sample material 3r , in particular of the first and / or the second polarization state, is guided at least partially free beam.

It is also possible that this affects the sample material 5 irradiated light 3e and / or that of the sample material 5 reflected light 3r , in particular of the first and / or the second polarization state, is a light beam, preferably wherein the light beam has a beam diameter between 10 μm and 10,000 μm at least in some areas.

3a shows schematically an enlarged section 12a of the 2a .

As in 3a shown is light 3e preferably by the reflective element 9 so on the sample material 5 irradiated that light 3r at the interface 13 formed from the sample material 5 and the reflective element 9 is reflected, in particular is totally reflected.

Here, as in 3a shown, particularly within the reflective element 9 , the angle (α) at which the light 3e on the sample material 5 is irradiated, equal to the angle (β) at which the light 3r of the sample material 5 is reflected.

For example, it is possible that, in particular within the reflection element 9 , the angle (α) at which the light 3e on the sample material 5 is irradiated, and the angle (β) at which the light 3r of the sample material 5 is reflected, between 0 ° and 90 °, preferably between 10 ° and 80 °. For example, the in 3a angles (α) and (β) shown equal 32 °.

The refractive index of the reflective element is advantageous 9 (n ₁ ) greater than the refractive index of the sample material 5 (n ₂ ). So it is possible that the refractive index of the reflective element 9 (n ₁ ) is between 2.0 and 4.0, preferably between 2.4 and 2.6, and / or that the refractive index of the sample material 5 (n ₂ ) is between 1.05 and 1.95, preferably between 1.25 and 1.75. For example, in 3a sample element shown 5 a refractive index (n ₂ ) of 1.33 and the in 3a Reflection element shown 9 has a refractive index (n ₁ ) of 2.59 at a wavelength of 633 nm. Preferably in the method and in the device 1 the dependency of the refractive index of the entire measurement setup, in particular the dependency of the refractive index of the sample material 5 and the reflective element 9 , negligible from the wavelength.

It is useful if the angle (α) is greater than or equal to the angle for which total reflection at the interface 13 formed from the sample material 5 and the reflective element 9 , especially for that on the sample material 5 irradiated light 3e , occurs.

In particular, the critical angle (Θ _c ) from which total reflection occurs is calculated as follows: $${\mathrm{\Theta }}_{\text{c}}=\text{arcsin}\left({\text{<figure-callout id="2" label="n" filenames="DE102019104556A1\_0006.png,DE102019104556A1\_0008.png" state="{{state}}">n</figure-callout>}}_2/{\text{n}}_1\right).$$

The critical angle (Θ _c ) is also referred to here in particular as the critical angle. From the critical angle (Θ _c ), the electromagnetic wave, in particular the incident light, can preferably 3e , no longer in the optically thinner medium, especially the sample material 5 penetrate, and is instead at the interface between the optically denser and the optically thinner medium, in particular at the interface 13 formed from the sample material 5 and the reflective element 9 , fully reflected. In particular, the angle of reflection is the same as the angle of incidence.

So it is possible that this is due to the sample material 5 irradiated light 3e , in particular due to the angle (α) at which the light hits the sample material 5 is irradiated in the sample material 5 is not capable of spreading.

The reflective element is advantageous 9 an optical fiber, in particular a Optical fiber in which light is guided due to total reflection. For example, such an optical waveguide is a prism or a fiber, in particular without a jacket.

Preferably the reflective element is 9 an ATR element, in particular an ATR crystal.

So it is possible that the reflective element 9 , preferably the ATR element, more preferably the ATR crystal, zinc selenide (ZnSe), germanium (Ge), thallium bromide iodide (KRS-5), silicon (Si), AMTIR (amorphous material transmitting infrared radiation), especially AMTIR-1 ( GeAsSe), and / or diamond.

Furthermore, it is also conceivable that, in particular in the case of FEWS infrared spectroscopy methods and / or in a FEWS infrared spectrometer, the ATR element comprises chalcogenide glass fibers.

It is also useful if the sample material 5 irradiated light 3e unpolarized light is preferred when that hits the sample material 5 irradiated light 3e has a polarization below 45 ° to the plane of incidence.

3b shows schematically an enlarged section 12b of the 3a .

As in 3b shown, the light is preferably so on the sample material 5 through the reflective element 9 irradiated that an electromagnetic wave on the surface of the reflective element 9 trains which in the sample material 5 penetrates, in particular wherein the field strength of the electromagnetic wave decreases exponentially. The electromagnetic wave is preferably on the surface of the reflection element 9 , in particular the field strength of which decreases exponentially, around a so-called decaying (evanescent) wave, which preferably occurs with total reflection at the interface 13 formed from the sample material 5 and the reflective element 9 arises. Especially when the sample material 5 now light is absorbed, the reflection of the light beam falls, especially that at the interface 13 formed from the sample material 5 and the reflective element 9 reflected light 3r , weaker, as the decaying (evanescent) wave, especially the evanescent field, passes through the sample material 5 Experiences losses. This is an exemplary distribution of the field strength in front of and behind the interface 13 formed from the sample material 5 and the reflective element 9 in 3b , particularly for an incident plane wave. As in 3b can be seen, the field strength drops in the sample material 5 exponentially.

FIGS. 4a to 4c show diagrams.

4a and 4b show by way of example the reflection at an interface between a reflection element made of ZnSe (n ₁ = 2.59) and the sample material water (n ₂ = 1.33) for the perpendicular polarization in 4a and for the parallel polarization in 4b in each case for the lossless case 15a and the lossy case 15b , in particular where the extinction coefficient (k) for the lossy case is k = 0.0508. The chart axes 14a show the angle of incidence in degrees and the diagram axes 14b show the reflectivity for the perpendicular polarization in 4a and for the parallel polarization in 4b . The diagram curves 15a and 15b were calculated as an example for the wavelength of 10 µm, since water strongly absorbs light in this wavelength range. How in particular 4a and 4b It can be seen that at an angle which is greater than the critical angle of total reflection, the attenuation for parallel polarized light is greater than the attenuation for perpendicularly polarized light. Furthermore, the two directions of polarization also have, in particular, a different phase offset (not shown here).

As in 4a and 4b In particular, the extinction coefficient of the sample material for parallel polarized light has a greater influence on the reflection than for perpendicularly polarized light. It is therefore to be expected in particular that a change in the extinction coefficient has a greater effect on the reflection of parallel polarized light on the reflection element than on the reflection of perpendicularly polarized light. In order to confirm this dependency in particular, the relative change in the reflection on the reflection element is determined below as a function of a relative change in the extinction coefficient of the sample material. In particular, the change in the extinction coefficient (k) is defined as follows: $$\mathrm{\Delta }\text{k}={\text{<figure-callout id="0" label="k" filenames="DE102019104556A1\_0007.png,DE102019104556A1\_0008.png" state="{{state}}">k</figure-callout>}}_0\cdot \mathrm{\epsilon }\text{f}ür\mathrm{\epsilon }<<1.$$

The changes in reflection are specifically defined as follows: $$\mathrm{\Delta }\text{R.}=\text{R.}\left({\text{k}}_0\right)-\text{R.}\left({\text{<figure-callout id="0" label="k" filenames="DE102019104556A1\_0007.png,DE102019104556A1\_0008.png" state="{{state}}">k</figure-callout>}}_0+\mathrm{\Delta }\text{k}\right)=\text{R.}\left({\text{k}}_0\right)-\text{R.}\left({\text{k}}_0\left(1+\mathrm{\epsilon }\right)\right).$$

Further, the relative change in reflection is defined as: $${\text{R.}}_{\text{rel}}=\mathrm{\Delta }\text{R / R}\left({\text{k}}_0\right).$$

In 4c is in particular this polarization dependence of the relative change in reflection for parallel polarized light 17a and perpendicularly polarized light 17b on the reflective element shown, in particular the diagram axis 14a shows the angle of incidence to the perpendicular on the interface in degrees and the diagram axis 14c shows the relative change in reflection on the reflective element. How 4c In particular, it can be seen that the influence of the extinction coefficient is greater the closer the angle of incidence, in particular the angle (α) at which the light is radiated onto the sample material, to the critical angle 16 the total reflection lies. The next can 4c it can be seen that, in particular, a variation in the extinction coefficient for the different polarizations of the light leads to relative changes in the reflection of different degrees. If the ratio between the reflection coefficients of both polarizations is now preferably formed, a dependency on the extinction coefficient remains. As explained above, this ratio formation is used in the method and the device for determining optical properties of a sample material. In particular, it is possible that, due to the formation of the ratio, some signal intensity is lost, preferably because there is a dependence on the extinction coefficient in both polarization states, but overall a signal is retained, preferably with the effects of the intensity noise of the light source and / or fluctuations in the measurement setup, such as set out above, reduced or eliminated.

It should be noted in particular that this dependency advantageously also exists for other polarization states than the parallel and the perpendicular polarization. However, the maximum difference between the polarizations becomes smaller, in particular in the case of other polarization states, so that signal strength is preferably consequently lost in the case of other polarizations. In other words, the distance between the maximum relative change in the reflection for polarization states other than that in FIG 4c shown lower, whereby the principal dependency is preferably retained. Furthermore, the 4c In particular, it can also be seen that the polarization dependence of the relative changes in the reflection on the reflection element have an angle dependency, but the angle setting is advantageously possible in a relatively large angle range, the angle range preferably between 0 ° and 5 °, more preferably between 0.5 ° and 3 °, above the critical angle of total reflection.

It should be pointed out here that it is also possible, for example, for the sample material 5 is liquid and / or solid. So it is possible that the sample material 5 for example, water, bacteria and / or solids. It is also conceivable that the sample material 5 one or more substances selected from the group: water, bacteria, viruses, solids, solvents, solvent mixtures, lacquer layers, polymer films, thermosets, body fluids, in particular blood, mono- or multicellular organisms, fungi, plants, in particular algae.

5a to 5c schematically show devices 1 in side view and in plan view.

In the 5a and in 5b shown device 1 includes a light source 2 , the mirror 6th , a reflective element 9 who have favourited polarizers 10a and 10b and the detector means 8a and 8b as well as an optical sump 18th .

Using the in the 5a and the 5b device shown 1 it is possible to carry out a method, preferably a spectroscopy method, more preferably an ATR infrared spectroscopy method, for determining optical properties of a sample material, in particular wherein the method comprises the following steps: a) determining a first intensity of light reflected from the sample material 3r a first polarization state; b) determining a second intensity of the light reflected from the sample material 3r a second polarization state; c) Formation of the ratio of the first intensity and the second intensity or vice versa. For the sake of clarity, the 5a and the 5b the sample material, which in particular is in direct contact with the reflective element 9 is applied, not shown.

Further it is possible that the device 1 , preferably a spectrometer, more preferably an ATR infrared spectrometer, a HATR infrared spectrometer, a FEWS infrared spectrometer and / or an FTIR infrared spectrometer.

With regard to the design of the light source 2 , the reflective element 9 and the detector devices 8a and 8b Reference is made here in particular to the statements above. In the 5a and 5b shown device 1 essentially corresponds to the in 2a and 2 B device shown with the difference that the device instead of the polarizer 10 the polarizers 10a and 10b comprises and instead of the detector device 8th the detector devices 8a and 8b . The in 5a and 5b The device shown also has the optical sump 18th .

As in 5a and 5b is shown by the reflective element 9 and / or the sample material 5 reflected light 3r , in particular that formed from the sample material at the interface 5 and the reflective element 9 reflected light 3r , preferably by means of the polarizers 10a and 10b separated into the first and second polarization states. The polarizers are preferably Brewster windows. Advantageously, through the Brewster window 10a the perpendicular polarization and through the Brewster window 10b the parallel polarization reflects or vice versa. The other polarizations are advantageously through the Brewster windows 10a and 10b transmitted and get into the optical sump 18th , in particular whereby this ensures that this does not interfere with the measurement result. Next, as in 5a and 5b shown, the intensities of the two polarization states, in particular the first and / or the second polarization state, then by means of the detector devices 8a and 8b certainly. The in 5a and 5b shown device 1 the detector device 8a to determine the intensity of the light reflected from the sample material 3r of the first polarization state and the detector device 8b to determine the intensity of the light reflected from the sample material 3r of the second polarization state.

It is then possible that the ratio of the intensities of the light reflected from the sample material 3r of the first polarization state and the second polarization state, in particular, reference being made in this regard to the above statements.

In particular for further noise suppression it is possible that at least one detector device 8a and or 8b is a synchronous detector (lock-in).

Using the in 5a and 5b device shown 1 it is possible, for example, to determine the intensity of the light reflected from the sample material, in particular that formed at the interface from the sample material and the reflection element 9 reflected light 3r to determine the first and the second polarization state simultaneously. In particular, due to the two detector devices, simultaneous detection of the two polarizations is possible, in particular with the sample material being excited uniformly, in particular with light of a polarization below 45 ° to the plane of incidence.

Furthermore, it is preferred that the light paths for the light reflected from the sample material 3r of the first and second polarization states, are substantially identical. The light paths preferably differ by less than 10 mm, preferably by less than 1 mm.

In the 5c shown device 1 corresponds to that in the 5a and 5b device shown 1 with the difference that on the one hand the sample material is an example 5 is shown, preferably the sample material 5 by means of a fixation unit 19th is fixed in such a way that the sample material 5 directly on or at the reflective element 9 is up or arranged. Preferably there is no further material, such as air, between the sample material 5 and the reflective element 9 arranged. Next is in the 5c also an arithmetic unit 11 to form the ratio of the intensities of the light reflected from the sample material 3r the first and the second polarization state shown. With regard to the design of this and the others in 5c The elements shown are referred to above.

So it is, as in 5c shown possible if the device 1 one of the following units comprises: a light source 2 , especially for irradiating light onto the sample material 5 by a reflective element 9 such that the light is formed at an interface from the sample material 5 and the reflective element 9 is reflected, especially totally, is reflected; - a reflective element 9 , preferably an ATR element, more preferably an ATR crystal, in particular wherein the sample material 5 an interface with the reflective element 9 trains; - a fixation unit 19th to fix the sample material 5 on the reflective element 9 ; - one or more mirrors 6th , especially for deflecting the light; - at least an optical swamp 18th .

It is also useful if the device 1 further comprises one of the following devices: one or more optical waveguides, preferably one or more fibers, more preferably one or more glass fibers, in particular for guiding the area-wise onto the sample material 5 irradiated light and / or from the sample material 5 reflected light 3r ; - One or more wavelength selectors, preferably one or more monochromators, in particular for the spectral isolation of a predetermined wavelength, preferably that of the sample material 5 irradiated light.

6th and 7th schematically show method steps for determining optical properties of a sample material.

6th schematically shows a flow diagram of a method 100 comprehensive the process steps 101 , 102 and 103 for determining the optical properties of a sample material. It is preferably the in 6th procedures carried out 100 a spectroscopic method, more preferably an ATR infrared spectroscopic method. Furthermore, it is also possible that the method is a HATR infrared spectroscopy method, a FEWS infrared spectroscopy method and / or an FTIR infrared spectroscopy method.

In the step 101 a first intensity of the sample material is determined reflected light of a first polarization state. In the step 102 a second intensity of the light of a second polarization state reflected by the sample material is determined. In the step 103 the ratio of the first intensity and the second intensity is formed or vice versa.

It is also advantageous if the step 103 after the steps 101 and 102 is carried out.

With regard to further possible configurations of the in 6th procedure shown 100 reference is made here to the above statements, in particular which were also presented in connection with the device explained above.

7th shows schematically a flow chart comprising the method steps 101 , 102 , 103 , 104 , 105 and 106 for determining the optical properties of a sample material. The steps 104 , 105 and 106 are optional and therefore shown in dashed lines.

In the optional step 104 light is radiated onto the sample material through a reflection element in such a way that the light is reflected, in particular totally reflected, at the interface formed from the sample material and the reflection element.

In the optional step 105 the light reflected by the sample material is then divided into the first polarization state and the second polarization state, preferably by means of at least one polarizer, more preferably by means of a first polarizer and a second polarizer.

The steps 101 , 102 and 103 correspond to the in 6th steps shown, so that reference is made to the above statements in this regard.

It is beneficial if in the step 103 the effects of the intensity noise of the light source are reduced, preferably eliminated, due to the formation of the ratio between the first intensity and the second intensity or vice versa.

In the optional step 106 Further method steps for further noise suppression, such as synchronous detection, can then take place.

It is also possible to use the method described above 100 and / or the device described above 1 for the spectral analysis, especially of the sample material. The spectral analysis, in particular of the sample material, is preferably based, as set out above, on total reflection, preferably frustrated total reflection.

So it is also possible that the method described above 100 and / or the device described above 1 is used for or for the suppression of the intensity noise from light sources, in particular in spectral analysis.

List of reference symbols

1

contraption

2

Light source

3

Light, ray of light

3e

irradiated light

3r

reflected light

4th

Beam splitter

5

Sample material

6th

(Deflection) mirror

7th

variable attenuator

8, 8a, 8b

Detector device (s)

9

Reflective element

10, 10a, 10b

Polarizer (s)

11

Arithmetic unit

12a, 12b

Cutout (s)

13

Interface

14a, 14b, 14c

Diagram axis (s)

15a, 15b

Diagram curve (s)

16

critical angle

17a, 17b

Diagram curve (s)

18th

optical sump

19th

Fixation unit

100

Procedure

101, 102, 103, 104, 105, 106

Procedural steps

1000

Measurement setup

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 7920264 B1 [0003]

Claims (15)

Method (100), preferably spectroscopy method, more preferably ATR infrared spectroscopy method, for determining optical properties of a sample material (5), comprising the following steps: a) determining (101) a first intensity of light (3r) reflected from the sample material (5) and having a first polarization state; b) determining (102) a second intensity of the light (3r) reflected by the sample material (5) in a second polarization state (102); c) formation of the ratio (103) of the first intensity and the second intensity or vice versa. Method (100) according to Claim 1 , characterized in that the method (100) further comprises the following step, in particular which is carried out before steps a) and b): splitting (105) the light (3r) reflected by the sample material (5) into the first polarization state and the second polarization state, preferably by means of at least one polarizer (10, 10a, 10b), more preferably by means of a first polarizer (10a) and a second polarizer (10b). Method (100) according to Claim 2 , characterized in that the at least one polarizer (10, 10a, 10b), in particular the first polarizer (10a) and the second polarizer (10b), is selected from the group: polarizer based on birefringence, preferably polarizing prism, more preferably Nicol's prism , Rochon prism, Glan-Thomson prism, polarizer based on dichroism, preferably J-foil and / or H-foil, and / or polarizer based on reflection, preferably Brewster window. The method (100) according to any one of the preceding claims, characterized in that the first and second polarization state differ, in particular that the first and the second polarization state are linearly polarized states with mutually perpendicular oscillation planes, wherein preferably the first polarization state parallel polarized light and the second Polarization state is perpendicularly polarized light. The method (100) according to one of the preceding claims, characterized in that the method (100) further has the following step, in particular which is carried out before steps a) and b): - irradiating (104) light (3e) onto the sample material (5) by a reflection element (9) in such a way that the light (3e) formed from the sample material (5) and the reflection element (9) is reflected, in particular totally reflected, at the interface (13). Method (100) according to Claim 5 , characterized in that the reflection element (9) is an ATR element, in particular an ATR crystal. Method (100) according to one of the Claims 5 or 6th , characterized in that the light (3e) irradiated onto the sample material (5) is unpolarized light, preferably that the light (3e) irradiated onto the sample material (5) has a polarization of less than 45 ° to the plane of incidence. Method (100) according to one of the Claims 5 to 7th , characterized in that the light (3e) irradiated onto the sample material (5) is light from the infrared wavelength range, preferably from the near and / or the middle and / or the far infrared range, more preferably light from the wavelength range between 0.8 µm and 1000 µm, even more preferably light from the wavelength range between 2.5 µm and 25 µm, further still more preferably light from the wavelength range between 8 µm and 12 µm. Method (100) according to one of the Claims 5 to 8th , characterized in that the light (3e) irradiated onto the sample material (5) is emitted by a light source (2), in particular wherein the light source (2) is selected from the group: laser, preferably semiconductor laser, more preferably quantum cascade laser (QCL) , and / or thermal radiators, preferably incandescent lamps, Nernst lamps, resistance heating elements made of silicon carbide or carbon arc lamps. Method (100) according to Claim 9 , characterized in that in step c) (103) due to the formation of the ratio of the first intensity and the second intensity or vice versa, the effects of the intensity noise of the light source (2), in particular on the measurement result, are reduced, preferably eliminated. Method (100) according to one of the preceding claims, characterized in that the light paths in step a) (101) and b) (102), in particular for the light (3r) of the first and second polarization states reflected from the sample material (5) , are essentially identical. Method (100) according to one of the preceding claims, characterized in that steps a) (101) and b) (102) take place simultaneously, in particular that the intensity of the light (3r) reflected from the sample material (5) of the first and the second polarization state can be determined simultaneously. Device (1), preferably a spectrometer, more preferably an ATR infrared spectrometer, for Determination of optical properties of a sample material (5) comprising: - at least one detector device (8, 8a, 8b) for determining a first intensity of light (3r) reflected by the sample material (5) in a first polarization state and for determining a second intensity of the Sample material (5) reflected light (3r) of a second polarization state; - At least one computing unit (11) for forming the ratio of the first intensity and the second intensity or vice versa. Device (1) according to Claim 13 , characterized in that the device has a first detector device (8a) for determining the first intensity of the light (3r) of the first polarization state reflected by the sample material (5) and a second detector device (8b) for determining the second intensity of the light (3r) from the sample material ( 5) has reflected light (3r) of the second polarization state. Device (1) according to one of the Claims 13 or 14th , characterized in that the device (1) further has at least one polarizer (10, 10a, 10b), in particular for splitting the light reflected from the sample material (5) into the first polarization state and the second polarization state, in particular that the device (1 ) a first polarizer (10a) for dividing the light (3r) reflected from the sample material (5) into the first polarization state and a second polarizer (10b) for dividing the light (3r) reflected from the sample material (5) into the second polarization state having.

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